1. Field of the Invention
The present invention relates to a novel racemoselective synthesis of ansa-metallocene compounds, novel ansa-metallocene compounds useful as components in polymerization catalysts, a process for the polymerization of olefins, particularly propylene, and olefin homopolymers, random and impact copolymers prepared by using the metallocene catalysts.
2. Background of the Art
Chiral ansa-metallocenes of transition metals of the groups three to six of the Periodic Table of Elements are increasingly being used as components for the stereospecific polymerization of olefins. For example, bridged substituted bis(indenyl) zirconium dichlorides are among the most important class of catalyst components for the manufacturing of isotactic polypropylene [Brintzinger, H. H.; Fischer, D.; Mühlhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143./Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi, F. Chem. Rev. 2000, 100, 1253/Pasquini, N. (Editor), Polypropylene Handbook, 2nd Ed. 2005, Carl-Hanser Verlag München]. Appropriately substituted ansa-metallocene complexes for the generation of isotactic polypropylene are generally obtained as mixtures of the racemic form and the undesired meso form from the processes of the prior art.
The classical synthesis of ansa-metallocenes to the prior art generally involves the deprotonation of a bis-indenyl-ligand by a strong base, followed by the reaction with zirconium tetrachloride or its solvent adducts. This classical path has two substantial drawbacks. Instead of the desired racemate, almost equivalent amounts of the mirror-symmetric meso diastereomer are formed in most cases. The meso isomer has to be removed from the mixture, either by means of destruction of the meso form, or removal by crystallization steps. The separation procedure generally lowers the yield of the amount of possible pure racemic complex. The other drawback is the low solubility of metallocene complexes, which leads to the use of large amounts of solvents for the final separation of the racemic and meso forms.
Several, so called “racemoselective” syntheses were described in the literature [see LoCoco, M. D.; Zhang, X.; Jordan, R. F., J. Am. Chem. Soc. 2004; 126 (46); 15231-15244 and cited lit.], comprising the use of alternative zirconium sources, which have to be synthesized prior to the manufacturing of the metallocene. WO2004/037840, WO99/15538 and DE10030638 describe multistage processes for preparing racemic metallocene complexes via biphenoxide- or bisphenoxide-substituted metallocenes as intermediates. These approaches lead to metallocenes substituted at zirconium with oxide or amide moieties. These intermediates have to be converted to the corresponding dichlorides in order to use them as catalyst components, thus adding extra steps to the synthesis.
U.S. Pat. No. 5,304,614 describes 2,4,7-substituted trialkyl-substituted metallocenes, which were obtained as mixtures between the racemic and the meso forms.
It is an object of this invention to provide novel ansa-metallocene structures for the selective preparation of the racemic complexes, which are virtually free of the meso isomer. Not to be bound by any particular theory, the inventors postulate that in order to achieve an intrinsic racemoselectivity, the hindrance of the formation of the meso form might be achieved by steric hindrance of the formation of the meso form. Attaching two large aromatic substituents to the indenyl-moiety in the 4- and in the 7-position should hinder the formation of the meso-form of the complexes. FIG. 1 illustrates this concept.
Another object of the present invention is to address the shortcoming of the state of the art metallocene compounds to provide metallocenes that afford high melting point, high molar mass homopolymers and high molar mass copolymers at high productivities when used as components of supported catalysts under industrially relevant polymerization conditions at temperatures of from 50° C. to 100° C.
Another objective of the present invention is to provide a process for the polymerization of olefins, particularly propylene, ethylene, and optionally one or more higher 1-olefins.
Furthermore, it is an objective of the present invention to provide olefin polymers, particularly propylene homopolymers, random copolymers of propylene with ethylene and/or higher 1-olefins, impact copolymers comprised of propylene, ethylene and/or optionally higher 1-olefins, and random impact copolymers comprised of propylene, ethylene and/or optionally higher 1-olefins.